Android

You are in the UK, so that is a good start. If you want longevity, I would prefer the Fairphone 6, which has excellent battery, decent cameras, and amazing custom ROM support (+ mobile Linux is developing too!), and it will also be very repairable, so you can easily replace the battery, ports, etc. as they wear out. They also have a long 5 year warranty + 8 years of promised software updates, quite a bit longer than both OnePlus and Google. The main downside for the Fairphone is no telephoto camera, which is a bit of a bummer, but the rest of the specs are very apt for the price €599, or £519 in the UK, and I would say the extended support + custom ROM support makes it an excellent deal.

The Pixels are pretty terrible in all respects (thermal issues, poor battery, decent cameras but not competitive, etc.), with their only redeeming quality being that you can install Graphene on them (awesome if you prioritise security), and even that advantage is going away with Motorola soon releasing supported devices! I would avoid Pixels for the most part, unless you can score a deal on a used Pixel 8 or 9 series (barely different from the 10 really, the 8 is nicer if you want rounded edges, 9 if you want to iPhone 4 style boxy shape), or you really want GrapheneOS now for its better security.

OnePlus has great cameras and far more performance than anyone would need in a phone (hell, you can emulate some PC games on it with GameNative), and it supports LineageOS too. I've also heard that the 13 in particular has excellent battery life. It's a pretty nice option if you want performance and cameras!

You might also want to look at some of the Sony Xperia devices if you want a) headphone jack! b) no notch/cutout! c) front-firing speakers d) great cameras and e) microSD card slot! The Xperia line is also relatively compact, if you want a smaller phone.